Beersmith tools tell me that in theory I could mash 27.5# at 1qt/# for 5.5gall @1.127 in my 50 qt cooler. It says I would have 0.04gallons left empty in the cooler, really not enough room to stir or even work with. It does look like the max in the 50qt though. If I dropped to 5G batch, same 27.5# @ 1qt per pound, it would yield OG of 1.14 again, just in theory.